This invention is directed to a filament dispenser cathode which has an exceptionally long life in a plasma discharge accomplished by drawing a filament of emissive material through the discharge chamber.
The cold cathode ion sources of the prior art are disadvantaged by the fact that they require high discharge voltage which causes the ions to be generated with a large energy spread. The fixed filament hot cathode sources of the prior art require large heater current and have only a short life. A hot filament discharge is well known for versatility in operation with many gases. But it is particularly difficult to provide a good life in such an ion source when the hot filament must operate with corrosive gas. Furthermore, it is desirable for its low energy spread which enables good beam formation. However, the short filament lifetime has been a major drawback which prevented the use of a hot filament ion source in production systems. Accordingly, there is need for a long life hot filament ion source.